Abstract 5061: Toxicological characterization and comparison of ATR inhibitors in mice
Authors: Joshua J. Deppas, Brian F. Kiesel, Jianxia Guo, Lora H. Rigatti, Joseph Latoche, Anthony Green, Paul Knizner, Christopher J. Bakkenist, Jan H. Beumer
Journal: Cancer Research (2023)

Abstract Cancer is often treated with DNA-damaging cytotoxic and ionizing radiation (IR) therapies. However, anticancer efficacy is limited by activation of DNA damage response (DDR) pathways that support DNA repair resulting in cancer cell survival. Disruption of DDR pathways may enhance cancer cell sensitivity to DNA-damaging therapies. Ataxia telangiectasia and Rad3 related (ATR) protein kinase, an apical initiator of DDR, is highly relied on by tumor cells and is critical for survival. Pharmacological ATR inhibitors (ATRi) can sensitize cancer cells to DNA damaging therapies. Although combining radiation therapies with ATRi may enhance anticancer efficacy, the resultant toxicity to normal organs is largely unknown. The ATRi furthest in development are the orally administered AZD6738 (ceralasertib), BAY-1895344 (elimusertib) and the intravenously administered M6620 (berzosertib, VX-970). We aimed to characterize and compare the preclinical toxicity of ATRi with and without total body irradiation (TBI) by pathology and complete blood counts (CBC). To determine the appropriate TBI dose for combination with ATRi, female balb/c mice (n=6) were grouped to receive 2, 4, 6 or 8 Gy. Within these cohorts, mice (n=2) were subdivided for euthanization times of 48, 72 and 96 h post TBI. Next, mice (N=5) were treated with a single dose of ATRi, 6 Gy TBI, the combination (TBI within 30 min of ATRi), or control. Mice were euthanized 48 h post treatment and blood was collected for analysis of CBC. Changes to body weight were documented and tissues with known sensitivities to radiation-related toxicity were collected for histopathology. Statistical analyses were performed using ANOVA with Tukey’s multiple comparisons test. A 6 Gy TBI dose and 48 h euthanasia time point were selected for investigation in combination studies with ATRi. TBI alone resulted in ~5% decreased body weight compared to vehicle controls. The addition of any ATRi appeared to ameliorate this loss, but not to a significant extent. TBI caused leukocytopenia and lymphocytopenia, which was not exacerbated by the addition of any ATRi. Neutrophilia was observed after ATRi alone and abolished by addition of TBI. TBI caused moderate toxicity in spleen, small intestine and bone marrow, and the addition of ATRi did not exacerbate these findings. AZD6738 caused moderate pericarditis and myocarditis, which was abrogated by the addition of IR. Collectively, ATRi administered alone are associated with neutrophilia at 48 h. AZD6738 appeared to be associated with cardiac toxicity, consistent with clinical observations of related CHK1 inhibitors. M6620 alone is associated with a significant decrease in lymphocytes compared to vehicle control, however in the setting of TBI, M6620 appears to ameliorate TBI-induced lymphocytopenia. This study demonstrated that the addition of ATRi did not increase toxicity associated with TBI in mice. Citation Format: Joshua J. Deppas, Brian F. Kiesel, Jianxia Guo, Lora H. Rigatti, Joseph Latoche, Anthony Green, Paul Knizner, Christopher J. Bakkenist, Jan H. Beumer. Toxicological characterization and comparison of ATR inhibitors in mice. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5061.